Magnetic material



July 12 1932- P. P. c|0FF| I MAGNETIC MATERIAL Filed July 51, 1950 ATTORNEY OOQQ Patented July 12, 1932 UNITED STATES PATENT OFFIE RAUL P. CIOIFI, OF BROOKLYN, NEW YORK, ASSIGNOR T BELL TELEPHONE LABORA- TORIES, INCORPORATED, OF NEW YORK, N, Y., A CORIORATION OF NEW YORK MAGNETIC Mammal Application filed July 31,

The present invention relates to heat treatments for developing desired magnetic properties in magnetic materials. a

An object of the invention is to dev'elo high permeability, low coercive force, low hysteresis loss and other desirable properties .in magnetic materials.

' Another object of the invention is to produce iron having higher maximum permeam bility than that of iron heretofore known.

A further object of the invention is to enhance the efliciency of hydrogenous atmospheres .as annealing media.

In applicants former application Serial No. 325,883, filed December 13, 1928 there are disclosed methods of securing desirable magnetic properties in magnetic materials by heat treating these material in hydrogenous atmospheres.

20 It has been found that a further improvement can be effected in the magnetic properties of such materials as are mentioned in the former application and in other materials, by including a certain amount of mois- :5 mm in the hydrogenous atmospheres in which the magnetic materials are treated. For instance, it has been possible to obtain a maximum permeability of 137,000 with iron as compared with the highestvalue of m 98,000 reviously reported. See page 225 of the Transactions of the American Electrochemical Society, vol. 56, 1929.

The resent specification is to be read in a the lig t of the specification of the said former application which is specifically, by reference, made a part of the present disclosure.

S ecific exam les of treatments and the resu ts accomplis lied thereby will now be described with reference to the accompanying drawing and tables.

7 For the purpose of the following detailed description the term moist hydrogen indicates a hydrogenous atmosphere consisting chiefly or partlyof hydrogen gas saturated with water vapor at room temperature. In the tests hereinafter described use has been made of various types of samples differing both'with respect to their shape and with respect to their-composition. The tests were 1930. Serial No. 471,988.

made with toroidal specimens which were cylinders of 1 inches outer diameter and inch high; those labeled thick had an inner diameter of /16 inches, those labeled thin had an inner diameter of 1 1/16 inches.

Figure 1 shows a curve A depicting the variation of the permeability of-a thick ring of Armco iron heated at 1500" C. for 12 hours in moist hydrogen. This sample had been cooled from 1500 C. to 880 (l-in about one hour, cooled to room temperature in about minutes and subsequently reannealed at 880 C. for two hours and cooled to room temperature in about 35 minutes. For purpose of comparison a curve B is given which shows the variation of the permeability of ordinary annealed iron. It is seen that the sample treated in moist hydrogen had acquired an initial permeability of 6,000and a maximum permeability of 131,000 at a magnetizing force at 0.044. gauss. Curves C and D, respectively, show the variation of the -magnetic induction for varying magnetizing fields for the same sample and for ordinary annealed iron.

Curves E and F of Fig.2 depict hysteresis centimeter per cycle for a maximum induction of 14,000 gauss and its coercive force was 0.05 gaussfor the same maximum induction of 14,000 gauss. At the same maximum induction' ordinary annealed iron has a hysteresis loss of 3,250 ergs per cubiccentimeter and a coercive force of- 0.67 gauss.

The subjoined table contains data on other samples of iron of the same composition and results obtained from their heat treatments. In this table column 1 contains an arbitrary number identifying the sample; column 2 designates the shape of the sample in accordance with the definition of shape previously given; column 3 indicates on the first line the temperature and duration of the first annealing, on the second line the temperature and-duration of the second annealing; column 4 the nature of the atmosphere used;

column 5 the initial permeability column 6 the maximum permeability and column 7 the magnetizing force at whichthe maximum permeability was determined.

5 The cooling rate used in the heat treatment of these samples was fairly uniform and consisted first in cooling from 1500" C. to 880 C. in about one hour from 880 C. to room temperature in about 35 minutes;

second in cooling after the reannealing treatment at 880 C. for the periods of time indicated for each sample, from 880 C. to room temperature in about 35 minutes. A reannealing temperature of 880 C. is mentioned because the reannealing treatment may advantageously be somewhat below the alphai'amma phase transformation point which for rmco iron-is at a temperature between 907 and 910 C. The table follows 2-- period was followed by cooling to room temperature at a rate of about 20 C. per minute. The following table gives the data found after each consecutive additional heat In another test Armco iron was melted in moist hydrogen, 0.10% of calcium boride was added to facilitate subsequent cold working after solidification, the melt was kept liquid Mafnet- 11 Nm Shape Heat treatment Atmosphere p, f n

1 This 1500 C.6hrs.....

0 %GC 26]1 57000 168 2 Thlnr ra.

3 Thin s hln 6 313? 39000 W 4 'r h M ?,0 6 37000 .218 s 'r .Ii' 0 'r a... T aggoc e fi m .1 I hickrln ..1 rs... moo o bin ififit e l'as T .1... o 1 hu 033 0 31. 13m 1 rs We] 101000 .0705 11 rlnl 1un 0. sm.-... mm m u Thick 150oo.sm..--. m 0.1 Means, m

There is evidence that to a certain extent with moist hydrogen the longer the heat treatment and the thicker the specimen the higher will be the maximum permeability. It appears that the use of a moist hydrogen atmosphere is particularly advantageous where o the article to be treated is of considerable thickness.

In another series of experiments a thick sample of Armco iron was first heated in moist hydrogen at. a temperature of about 1500 C. for 12 hours and then cooled from 1500 to about 880 C. in eight minutes, the cooling from 880 C. to room temperature taking about 25 minutes. The iron was found to have an initial permeability of 1950 and w a maximum permeability of 25,000. The

same sample was then reannealed at about 880 C. for additional periods of time, the annealin being interrupted after these periods or enabling the taking of magnetic measurements. All the annealing was efiected 1n moist hydrogenmnd each anneal ng for 16 hours and cooled to room temperature in 4 hours. Then the material was cold rolled from inch to 4;, inch and a thin ring specimen was prepared. This specimen was heat treated at 880 C. in moist hydrogen for 6 hours and cooled to room temperature at an avera e cooling rate of about 20 0. per minute. and a maximum permeability of 25,400 at a maximum force of 0.36 gauss.

Ordinary cold rolled steel containing about 0.1% carbon was heat treated in moist hydrogen for 12 hours at a temperature of 1500 C. and cooled to room temperature in about one hour. It was found to have an initial permeability of 1400 and a maximum permeability of 33,000 at a magnetizing force of 0.23 gaufls.

An iron-cobalt alloy comprising about iron and 50% cobalt was heat treated in moist hydrogen at 1440 C. for 12 hours, cooled to room temperature at an avera e rate of about 40 C. per minute, reanneal at 940 C. in

t had an initial permeability of 1600 moist hydrogen for 2hours and slowly cooled. Such an alloy has a phase transformation point at about 980 C. It exhibited an initial permeability of 600 and a maximum permeability of 7400, whereas an alloy of the same composition, if heat treated in the ordinary manner exhibits an initial perme-- ability of only 600 and a maximum bilit of only 4000.

I ron as used herein refers to the metallic element in a relatively pure form and does not include alloys of iron or compositions having other elements added thereto as essential constituents.

What is claimed is:

1. 'The method of increasing the efiiciency of hydrogenous atmospheres as annealing media for magnetic materials at temperatures above about 1000 C., which method comprises adding water vapor to the hydrogenous atmosphere.

2. The method of preparing magnetic materials with desirable magnetic properties in desired shape for use, which method comprises (a) heating the material in hydrogen, (6) cooling the material to a much lower tem= perature, (0) working the material mechanically into the desired shape, and (d) reheating the material to a temperature below the permeaalpha-gamma transformation point if the material has such a point above room temperature, said method being further characterized in this that the hydrogen in which the material is heat treated contains water vapor.

3. A method of improving the magnetic properties of magnetic materials which comprises heating the materials at a temperature above 1000 C. in a hydrogenous atmosphere containing water vapor. v

4. A method of improving the magnetic properties of magnetic materials which comprises heating the materials at temperatures close to their melting points in an atmosphere containing hydrogen and water vapor;

5. A method of improving the magnetic properties of magnetic materials which comprises heating the materials at a temperature above 1000 C. in a hydrogenous atmosphere saturated with water vapor at room temperature.

and cooling the material to room temperature characterized in this that at least one of said heat treatments takes place in an atmosphere containing hydrogen and Water vapor.

9. The method of treatinga material com- I prising at least 95% iron, which comprises heating the material in a hydrogcnous atmosphere at a temperature near its melting point, cooling said material to about 880 C.,

heating the material at a temperature of 6. As anew article of manufacture, mag

netic iron having a maximum permeability 

